1. Field of the Invention
The present invention relates to the preparation and insertion of dental appliances, such as removable partial dentures and the like, and particularly to a device for verifying parallelism of abutment teeth for insertion of the dental appliance.
2. Description of the Related Art
For the accurate placement of a dental appliance, such as a fixed partial denture, for example, the parallelism of the axial walls of abutment teeth is a fundamental concern. The path of insertion of a dental appliance is expressed by the angle between the horizontal plane through the teeth and the plane tangent to the axial wall of the abutment teeth. When the abutment teeth do not have a particular inclination, the path of insertion of the dental appliance is approximately 90°. When an abutment tooth is inclined mesially, removal of an inordinate amount of tooth substance can threaten the integrity of the dental pulp. The path of insertion of the dental appliance in this case will be less than 90° and depends on the inclination of the abutment tooth. When the inclination angle of the abutment tooth is less, so is the angle of the path of insertion, thus jeopardizing the parallelism with the axial wall of the other abutment tooth.
In treatment planning, preemptive measures are instituted to determine the path of insertion to ensure parallel axial walls of abutment teeth. Commonly, for inspection by the indirect method, intraoral impressions are made and a cast is poured. The cast is examined on a laboratory surveyor and the parallelism of the abutment teeth is verified. This technique, however, suffers from the following disadvantages: it requires additional visits before the final impression is made; there is no certainty that this second appointment will ensure parallelism because the exact location and amount of tooth structure for removal requires an additional impression; and conservatism is difficult.
Conversely, direct methods use devices referred to as intraoral and extraoral parallelographs. The intraoral parallelographs have the disadvantage of an additional visit for device preparation and the extraoral parallelographs have limited stability. It would be desirable to be able to determine the parallelism directly, easily and efficiently. Thus, a device for verifying parallelism of abutment teeth for dental appliance insertion solving the aforementioned problems is desired.